Compact circuit breaker

ABSTRACT

A compact electric circuit breaker with high current carrying ability is disclosed. This circuit breaker utilizes compact means to achieve high contact pressure necessary for high current carrying ability, and, in addition, utilizes a mechanical arrangement occupying a minimum amount of space and including a minimum number of force reducing members which cooperate to permit a relatively low trip force to actuate the circuit breaker and thus open the circuit upon the occurrence of a particular condition such as a current overload.

United States Patent Powell Jan. 15, 1974 COMPACT CIRCUIT BREAKER [75] Inventor: David B. Powell, Bristol, Conn. Primary Exammer Harold Broome Attorney-Robert T. Casey et al. [73] Assignee: General Electric Company, New

York, [57 ABSTRACT [22] Filed: Dec. 27, 1972 A compact electric circuit breaker with high current carrying ability is disclosed. This circuit breaker uti- [21] Appl' 318992 lizes compact means to achieve high contact pressure necessary for high current carrying ability, and, in ad- [52] US. Cl 335/169, 335/22, 335/191 dition, utilizes a mechanical arrangement occupying a [51] Int. Cl. H01h 9/24 minimum amount of space and including a minimum {58] Field of Search 335/167, 169, 170, number of force reducing members which cooperate 335/171, 172, 173, 174, 190,191, 192,22 to permit a relatively low trip force to actuate the circuit breaker and thus open the circuit upon the occur- {56] References Cited rcnce of a particular condition such as a current over- UNlTED STATES PATENTS load' 3,731,239 5/1973 Ellenberger 335/167 9 Claims, 9 Drawing Figures mmnn m1 1 5 1914 3.786382 sum 1 or 5 km n I k] 'm "1 J5 E y 51% n r i HMT ei IE 1]! I "Ai ENTEUJAH 15 m4 3 786 382 sum 2 ur 5 FIG. 3

PAIENIEuJms m4 3.786 382 sum 5 or 5 FIG. 7C

COMPACT CIRCUIT BREAKER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to electric circuit breakers and more particularly to compact electric circuit breakers of the type having a high ratio of contact pressure to trip force.

2. Description of the Prior Art Circuit breakers of the type disclosed include an onoff switch comprising a pair of separable contacts which are electrically connected to an electric circuit by means of screw-type r plug-in type terminals. The contacts are moved into and out of engagement by an operating mechanism. When the contacts are brought into engagement, the circuit breaker is in an On condition and current may pass therethrough. The circuit breaker is in either an Off condition or a Tripped condition when the contacts are separated, and no current may pass therethrough. If the separation of the contacts is effected through manual actuation of the operating mechanism, the circuit breaker is in the Off condition. The circuit breaker may be provided with means for sensing a particular electrical condition, e.g., a current overload condition. When the circuit breaker is in the On condition, upon the occurrence of that particular electrical condition, the operating mechanism will be automatically actuated, or tripped, so that the contacts separate and the circuit breaker will then be in the Tripped condition.

Generally, electric circuit breakers having a relatively high current carrying capacity require the application of greater contact pressure to the separable contacts during engagement in order to maintain necessary low contact resistance and avoid excessive heating. In order to achieve the desired contact pressure, many prior art circuit breakers employed an operating mechanism utilizing overcenter springs to apply the necessary force to contact members carrying respective contacts. The overcenter springs also applied the force necessary to separate the contacts when desired to do so. In applying each of these distinct forces, the overcenter springs are required to change their orientations with such movements requiring increased space for their operation. Additionally, with increasing contact pressure requirements, these overcenter springs were required to exert greater forces and the springs themselves necessarily became stronger and bulkier, further requiring additional space. In order to interrupt application of the spring force on the contact members and thereby permit the contacts to be disengaged in response to a predetermined electrical condition, trip means were employed to provide a direct forceful action against the operating mechanism. Early trip means utilized a relatively large trip force against the operating mechanism and consequently such trip means were comprised of bulky, massive members of relatively high strength. Low trip force mechanisms have been subsequently developed which required a relatively low trip force to overcome a relatively high contact force. The component members of such a low trip force mechanism could have less massive, lower strength structures. However, such mechanisms employed a relatively large number of force reducing members with consequent increased complexity, cost, and likelihood of malfunctioninglt' has become desirable, in order to provide a physically more compact, low trip force circuit breaker having relatively high current carrying ability, to develop a circuit breaker mechanism whose component parts are simpler in structure, fewer in number, and having a more compact arrange ment than was known in the prior art.

By the present invention, the deficiencies of the prior art have been overcome and a compact circuit breaker is provided which employs compact means to develop high contact pressure and further employs simplified operating and trip means, requiring a relatively small space, to effect engagement of the contacts and to effect automatic disengagement of the contacts with the application of a relatively small trip force.

OBJECTS OF THE INVENTION It is an object of this invention to provide a relatively compact electric circuit breaker characterized by relatively high contact pressure which achieves relatively high current carrying ability.

It is also an object of this invention to provide such a compact circuit breaker employing in combination therewith a simple compact compression spring which takes up a minimum amount of space and yet is capable of producing a relatively high contact pressure.

It is additionally an object to provide such an electric circuit breaker whose operating mechanism requires a relatively low trip force to permit disengagement of the contacts and employs trip means having a minimal number of force reducing linkage members.

It is a further object of this invention to structurally integrate the trip means and operating means to achieve a more compact over-all structure.

SUMMARY OF THE INVENTION The invention disclosed overcomes theabovementioned disadvantages and achieves the aforementioned objects through the use of a circuit breaker having an insulating casing pivotally mounting a handle. The casing contains a stationary contact member and a contact member which is movable into and out of engagement with the stationary contact member. Operating spring means are provided to act on the movable contact member. A collapsible connecting member is em ployed to connect the handle and the movable contact member. The connecting member comprises first and second pivotally interconnected links and a latch member pivotally connected to the second link and releasably engaging the first link. A trip member, pivotally mounted in the casing is biased toward the connecting member. Means is also provided for normally restraining the trip member in a predetermined position out of contact with the connecting member. Releasing means mounted in the casing is operable to cause releasing movement of the means which normally restrain the trip member. Upon actuation of the releasing means, release of the restraining means occurs so that the trip member is moved into engagement with the latch member to effect release of the first link from the latch and thereby permit collapse of the connecting member by the operating spring means acting on the movable contact member.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, FIG. 1 is a plan view of a two-pole circuit breaker incorporating the invention, a portion of the insulating casing thereof being broken away to expose one pole or electrically conductive path through the circuit breaker.

FIG. 2 is a side elevation view in section, taken along the line 22 of FIG. 1 and showing the electrically conductive path illustrated in FIG. 1 wherein the circuit breaker is in the On condition.

FIG. 3 is an enlarged side elevation view in section, taken along the line 3-3 of FIG. 1, but showing the circuit breaker in the tripped condition.

FIG. 4 is a view similar to FIG. 3, showing the circuit breaker in the Off-Reset condition.

FIG. 5 is a view similar to FIG. 3, showing the circuit breaker in the On" condition.

FIG. 6 is a perspective view of the operating mechanism and a portion of the accompanying support structure employed in the circuit breaker shown in FIGS. 3-5.

FIGS. 7a, 7b, and 7c illustrate individual components of the operating mechanism shown in FIG. 6. FIG. 7a illustrates the first link of the connecting member; FIG. 7b illustrates the second link of the connecting member; and FIG. 7c illustrates the latch member.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2, the invention is shown as incorporated in a circuit breaker having an insulating casing 1 comprising a base portion 3 and a cover portion 5. The base portion 3 includes a thin barrier 6 of insulating material at one end thereof which extends the full height of the casing. While a two-pole circuit breaker is shown, the structure and operation of one pole only will be described for simplicity, it being understood that the structure of both poles is essentially identical.

A screw-type terminal 7 and a plug-in type terminal 9 are fixedly disposed in the casing 1 (See FIG. 2) so as to provide electrical connection between the circuit breaker and the circuit in which the circuit breaker is to be used. The terminals 7 and 9 are electrically connected respectively to movable and stationary contacts 73 and 87 which contacts provide means for achieving an electrically continuous path through the circuit breaker. The circuit breaker includes a support structure 11 or frame which supports an operating mechanism 13 (both shown in FIG. 6). Trip means 15 functions in response to the occurrence of-a particular condition, such as a current overload condition, to protect the circuit from damage by excess current.

Referring now to FIG. 6, the support structure 11 comprises a pair of substantially similar, planar support or frame members 17 which are aligned and disposed in parallel spaced-apart relation within a central chamber (See FIG. 1) of the casing base portion 3. The support of frame members 17 are interconnected by a lateral connecting member 21 which serves, among other purposes, to maintain the aligned, spaced-apart orientation of the support members 17. The support or frame members 17 each have identical guide slots 36 for guiding an element of the operating mechanism 13, as will be discussed later. Additionally, each of the support or frame members has a projection 18 extending upwardly therefrom and having a hole 19 therein. A pin 23, extending through the holes 19, spans the support or frame members 17 and serves to mount the operating mechanism 13.

The operating mechanism 13 includes a spring biased handle 25 and a collapsible connecting member 37 pivotally connected to the handle by pin 35. The handle 25 is rotatably supported on the pin 23. A coil spring 27, also supported on pin 23, engages both the handle 25 and a notch in one of the support members 17 thereby to bias the handle in a clockwise direction. The handle 25 has an elongated end 31 with an elongated hole 33 therein for receiving a pin 35 which extends from the handle 25 through the pair of aligned guide slots 36 in the support members or frame 17. A pair of small triangular projections 34a. 34b are disposed on one face of the elongated end 31, on opposite sides of the hole 33 (See FIG. 3).

In order to transmit motion from the handle 25 to the movable contact 73 so that it may be brought into and out of engagement with the fixed contact 87, the collapsible, connecting member 37 is employed to connect the handle 25 to a movable contact arm 71 supporting the movable contact 73 (shown in FIG. 2). The connecting member 37, mounted at one end thereof to pin 35, is disposed between the support or frame members 17. The connecting member 37 comprises a pair of pivotally connected links 39, 49 which can be releasably latched together so that motion and force may be transmitted from the handle 25 through the pin 35 and along the length of the links tothe movable contact arm 71 to bring the contacts 73, 87 into engagement with each other. It is desirable to be able to interrupt the transmission of such force and motion so that the contacts may be disengaged from each other. Thus, the links are constructed in accordance with the invention in such a way that they may be unlatched to permit collapse of the connecting member and disengagement of the contacts.

The first link 39 comprises a pair of identical aligned link members 39a, 39b, one of which is shown more clearly in FIG. 7a. Each of the link members has a hole 41 therein adjacent one end thereof for receiving pin 35. These link members 39a, 39b adjacent the opposite end thereof, each have a hole 43 for receiving a pin 45 and also have a notch 47 disposed proximate the hole 43.

Referring to FIG. 7b, the second link 49 is a channelshaped member having a pair of opposed, similar flanges 49a, 49b extending from a central portion 50. Each of the flanges 49a, 49b has a hole 51 disposed therein. The holes 51 receive and support the pin 45 with the first link members 39a, 39b being mounted on the pin 45 between the flanges 49a, 49b.

The links 39 and 49, so mounted, can readily pivot with respect to each other about the pin 45. However, since it is desirable to be able to defeatably transmit motion through the links, it is necessary that these links be releasably engageable with respect to each other. In order to provide such releasable engagement of the links 39, 49, a latch 55, which is most clearly shown in FIG. 70, is pivotally mounted to the second link 49 and releasably engages the first link 39. The latch 55 is a channel-shaped member dimensioned so that it can be nested within the channel of the second link 49. The latch comprises a central flange 56 having a pair of similar, side flanges 57 extending perpendicularly from the opposed edges thereof to form a channel-like structure. A pair of aligned holes 58 is disposed in the side flanges 57. In order to mount the latch 55 with respect to the second link 49, the latch holes 58 are aligned with a second pair of holes 59 in the second link flanges 49a, 49b (See FIG. 7b) and a pin 61 (See FIG. 6) is extended through these two pairs of aligned holes 58, 59. The latchs central flange 56 has an extension 63 having a pair of projections 65 extending laterally from opposite sides thereof and further having an obliquely oriented projection 67 extending from the end thereof. The width of the lateral projections 65 is intended to be noticeably less than the width of the notches 47 with which projections 65 will mate. The lateral projections 65 extend beyond the width of the channel of link 49. Thus, a pair of cutout portions 53 (See FIGS. 6, 7b) are disposed in the second link 49 to provide clearance for movement of the projections 65 with respect thereto.

As shown in FIG. 6, when the connecting member is assembled, the latch 55 is oriented with respect to the second link 49 so that the projection 67 extends above and around the pin 45 while the lateral latch projections 65 enter into a loose, releasable engagement with the notches 47 in the first link members 39a, 39b so that limited relative movement of the engaged links is possible. When the circuit breaker is assembled, a switch-closing force applied to the handle and transmitted to the connecting member 37 moves the contact arm 71 to closed position. When this occurs, the inertia or momentum of the inter-connected links which form the member 37 go through center to a slightly over-set or partially collapsed condition asshown. This overset or slightly buckled condition is permitted by the loose engagement of latch 55 with links 39. Since further collapse is normally prevented by the latch 55, the links still normally form a rigid member, and hold the contacts closed.

Unlatching of the engaged links 39, 49 so as to permit collapse of the links with respect to each other, is provided by applying a force against the latch 55. More specifically, a force is applied against the inner surface 670 of oblique projection 67, thereby to move the latch projections 65 out of engagement with the notches 47. A mechanical advantage is available during the unlatching process to assist in unlatching. This mechanical advantage arises because the distance from the pin 61, about whichthe latch pivots, to the point of engagement between the latch projections 65 and notches 47 is less than the distance from the same pin 61 to the oblique projection 67 where force is applied to achieve unlatching.

Attempts have been made to collapse prior art connecting members not employing latches, by direct application of force to the joint joining the respective links of such connecting members. Such arrangements have been difficult if not impossible to collapse because a relatively large force has been required if the links are in an under-set condition. If the links go to an overset condition in such a device, unwanted tripping or opening would occur. Also, it is very difficult, if not impossible, to make a device on a mass-production basis, in which the links will always be on dead center. The use of a latch 55 as described above wherein a disengaging force is applied to the latch rather than a collapsing force applied directly to the joint connecting the links, permits a much smaller force to be used.

It is apparent that, in addition to the use of a latch, both the aforementioned mechanical advantage and the tendency of the links to assume a slightly collapsed orientation upon application of the aforementioned switch-closing force to the connecting member further contribute to the ease of collapse of the collapsing member and the consequent need for a relatively small collapse-initiating force.

A torsion spring 69 is disposed on the pin 45 between the first link members 39a, 39b. The coiled portion of the spring 69 is of sufficient length to keep the link members 39a, 39b spaced apart from each other and to align their notches 47 with the projections 65. The spring 69 includes a pair of extension arms 69a, 69b. The arm 69a extends from the one end of the coil portion of spring 69 into a biasing contact with pin 35 while arm 69b extends from the other end of that coil into biasing contact with the latch 55. The net effect of the biasing action of this spring is to move the links 39, 49 toward an aligned or stranghtened position wherein similar edges 48a, 48b, of links 39a, 39b near the notched end, abut the edge 50a of the central portion 50 of link 49. It is when this abutting of the edges occurs that the latch projections 65 willloosely, releasably engage the notches 47 Referring now to FIGS. 1 and 2, the movable contact arm 71 supports a contact 73 at a first end 71a thereof and is electrically connected at a second end 71b to an electrical conductor 74 which is in turn connected to terminal 7. In order to transmit an opening or closing movement from operating mechanism 13 to the contact arm 71, contact arm 71 is connected to the second link 49. More specifically, arm 71 is pivotally supported intermediate its ends at hole 75 by pin 61 which extends through the hole 75. To assist in guiding that movement of arm 71, a guide pin 77 is provided which extends through a notch 79 in arm 71 near the second arm end 71b. Pin 77 is adapted to move within a pair of opposed aligned slots 81 disposed in the casing base portion 3, thus restricting the longitudinal movement of the arm 71 and the connecting member 37 attached thereto.

A relatively compact simple compression spring 83, disposed within the casing 1 between the pins 61 and 77 and immediately subadjacent the arm 71, aids in both engagement and disengagement of the movable and stationary contacts 73 and 87. During the process in which the contacts 73 and 87 become engaged, the spring 83 applies a force to the contact arm 71 to force the contacts more tightly together, as will be explained in more detail under Operation. During the process of disengaging the contacts, the same spring 83, acting in the same direction at the same point on the contact arm 71, applies a similar force against the contact arm 71 to separate the contacts.

The contact arm-spring arrangement here described is advantageous over the prior art partly because it permits the use of a simple compression spring rather than an over-center acting spring. Over-center acting springs are inefficient when used in circuit breakers because only a relatively small component of the force that such a spring exerts is exerted to effect engagement of the contacts, while another component of the spring force is held in reverse to effect disengagement of the contacts. Moreover, the over-center spring changes its orientation to exert the different forces at different times. The simple compression spring comtemplated for use in combination with this invention is more efficient in that this sample compression spring always maintains the same orientation, so that the same spring force is always acting in the same direction. There is thus no need to have a reserve" force component in the spring. and the full capability of the spring may be utilized whenever the spring is acting. This permits a compactness not permitted with an over-center spring. Additionally, since the compression spring does not have to change its orientation during operation of the circuit breaker, additional space savings may be possible.

A stationary conductor 85 supports a contact 87 at a first end 85a thereof, and is electrically connected at a second end 85b thereof to an electrical conductor 89 which is connected to a terminal 9. The stationary conductor 85 is fixedly disposed in the base portion 3 of insulated casing 1 so that the fixed contact 87 is aligned for engagement with contact 73 upon guided down ward movement of movable arm 71 to its fullest extent.

When the circuit breaker is in the On condition (See FIG. 5), the connecting member 37 is in a rigid, but slightly collapsed orientation and the respective contacts are engaged. When predetermined circuit conditions (e.g., overload condition) occur, the trip means automatically responds to effect collapse of the connecting member 37 so as to separate the abutting contacts 73 and 87, thus interrupting the circuit. Referring to FIG. 3, the trip means 15 is seen to include a trip member 91 which is intended to apply a force against the oblique projection 67 to achieve the desired collapse of the connecting member 37. The trip member 91 is a planar member, having first and second projections 93 and 95. The trip member 91 is pivotally mounted at hole 97 by being rigidly attached to pin 23. The member 91 is disposed between the handle end 31 and the handle biasing spring 27 as best shown in FIG. 6. Mounting the trip member 91 by rigid attachment to pin 23 which also pivotally mounts the operating mechanism, in effect structurally integrates the trip means and the operating mechanism, to achieve a physically more compact arrangement than disclosed by the prior art. In prior art circuit breaker mechanisms having a comparable trip member, the trip member was mounted at some point distinct from the pivot corre sponding to pin 23 (e.g., handle pivot) and in most cases below it. Thus, a dimensionally smaller casing may be utilized with the circuit breaker incorporating the present invention.

The trip member 91 is biased counter-clockwise as shown by tripping spring. The trip member 91 when released, engages projection 67 on the latch, to effect collapse of the connecting member and opening of the contacts as previously described.

The trip member 91 is provided with a slot 99 which receives the pin 35 and the small triangular projections 34a, 34b of the handle 25 (See FIG. 3). The edge 25a of the handle 25 contacts the edge 99a of the trip member 91 under reset conditions, to effect resetting movement of the trip member 91.

The trip means 15 also includes a trip bar 101 having a pair of arms 103 supported on one surface thereof. The arms 103 are adapted to mate with aligned slots 105 (See FIG. 1) on opposed sides of the base portion 3 of the casing. The trip bar 101 also includes an extension arrn 107 disposed intermediate the ends thereof and extending downwardly into the base portion 3 of the casing. The extension arm 107 includes a slot 109 therein for engaging and retaining the first projection 93 of the trip member 91. The extension arm 107 also includes a hole 111 for receiving one end of a trip bar return spring 113. The other end of the spring 113 is connected to the lateral connecting member 21 of the support structure 11 (See also, FIG. 3).

In order to provide automatic response by the circuit breaker to a current overload condition, heat responsive trip means is provided which comprises a cantilever-mounted bimetallic member 115, carrying a calibration screw 117 at the free end thereof, disposed near the conductor 74. The bimetallic member 115 bends or warps so to move its free end in a clockwise direction in response to heat generated by current passing through conductor 74. On the occurrence of excess current, the screw 117 moves into contact with a surface on the trip bar 101 to cause corresponding movement thereof, causing the extension arm 107 to rotate out of engagement with the trip member 91 at slot 109.

To provide automatic response by the circuit breaker to fast excess current rise such as during short circuit conditions, magnetic trip means is provided. The magnetic trip means includes a spring biased armature 119 pivotally mounted in the casing base portion 3 between the bimetallic member 115 and the trip bar 101. A magnetic field piece 120, disposed at one side of the conductor 74, develops a magnetic field upon occurrence of a short circuit condition. This magnetic field causes rotation of the armature 119 into the trip bar 101 to cause corresponding movement thereof and thus disengagement of the trip member 91 from the trip bar 101.

A trip spring 121 (See also FIG. 6) is disposed on a trip spring guide rod 123 which extends between the lateral connecting member 21 of the support structure 11 and a notch 126 in the trip member 91. The trip spring 121 exerts a biasing force against the trip member 91. Upon disengagement of the first projection 93 of the trip member 91 from the slot 109 in the extension arm 107 of the trip bar 101, the biasing force of spring 121 urges the trip member 91 to move in a counter-clockwise direction about hole 19 in the frames 17 so that the second projection moves into abutting contact with the projection 67 of the latch with sufficient force to cause unlatching of the links 39 and 49 and produce collapsing of the connecting member 37.

The trip means herein employed has a simple structure employing a minimum number of parts. The arrangement of the connecting member 37, with its inherent ease of collapse, permits the trip means to execute its function of automatically collapsing the connecting member upon the occurrence of certain predetermined conditions, with only a relatively small force. Since the force needed to be applied is relatively small, the structure of the component members of the trip means need not be as large as they would otherwise have to be.

Referring to FIGS. 3, 4, and 5, the operation of the invention can be readily visualized. As can be seen in FIG. 3, where the circuit breaker mechanism is in a Tripped mode or condition, the contacts 73 and 87 are separated from each other and the connecting member 37 is collapsed because the latch member 55 has been moved out of engagement with the first link 39. The operating spring 83 and the trip spring 121 are in relatively relaxed positions and the trip member 91 is disengaged from the trip bar 101.

To put the circuit breaker in the Off-Reset mode or condition, so that it may be manually operated as a normal switch controlling passage of current through the circuit, the handle 25 is rotated clockwise from the position shown in FIG. 3, through a relatively small arcuate distance, to the position shown in FIG. 4. During this handle rotation the edge 25a of the handle 25, moves into abutting contact with the edge 99a of the trip member 91 moving it clockwise about the axis of pin 23, to the position shown in FIG. 4 where the first projection 93 of the trip member engages the trip bar 101 at the slot 109. This rotation of the cradle member effects counter-clockwise rotation of the trip spring guide rod 123 about the lateral connecting member 21 whereby the trip spring 121 supported therein is compressed. Thus, with the trip member 91 in the Off- Reset condition, the trip spring 121 continuously acts against the trip member 91, tending to urge it toward a counter-clockwise rotation about its pivotal support. Note, however, that the force of the trip spring 121 is entirely independent of the contact-operating mechamsm.

Moving the handle 25 into the Off-Reset condition shown in FIG. 4 also puts the collapsible member 37 into an extended condition so that the projections 65 on the latch 55 engage the notches 47 in the first link 39. With the links 39, 49 so latched, the connecting member 37 can act as a single, substantially rigid member, which may transmit motion and force therethrough. Forces and motion applied at the uppermost end of the connecting member 37 by rotating the handle 25 will thus be transmitted throughout the length of the connecting member 37 to the movable contact arm 71.

To move the circuit breaker mechanism from the Off-Reset position to the On position shown in FIG. 5, the handle 25 is rotated counter-clockwise to the position shown in FIG. 5. During this rotation, the trip member 91 remains engaged to the trip bar 101 while the connecting member 37 is swing downwardly carrying the movable contact arm 71 with it.

It is important to note that the downward movement of the contact arm 71 is characterized by two sequential, oppositely directed, rotational motions. Initially, the contact end 71a of the arm 71 is caused to pivot in a clockwise direction about a fulcrum point to the left of the operating spring 83 (which exerts an upwardly directed resisting force) while the connecting member 37 applies a downward force on the contact arm 71 at pin 61. The contact 73 engages the contact 87 before the handle 25 is swing fully through the extent of its potential arc of movement. After the contacts 73, 87 have become engaged, continued rotation of the handle 25 in a counter-clockwise direction produces the second of the aforementioned rotational motions wherein the fulcrum point shifts to the right of the operating spring 83 to the point of engagement of the contacts 73, 87. The contact arm 71, near the end 71b, then moves in a counterclockwise direction about this second fulcrum point, thereby causing further compression of the spring 83. During this second motion, the relation of the forces acting on the contact arm is such that the downward force applied to the arm 71 at pin 61 is counteracted by a resistant force of the operating spring 83 acting upward so that the contact arm 71 has a tendency toward rotation about pin 61 in a counterclockwise direction, thereby imparting additional downward force on the contact 73 at contact 87 to achieve additional contact pressure with accompanying lower contact resistance and improved current carrying ability of engaged contacts. These forces act on the connecting member 37 so as to maintain the connecting member in its slightly collapsed position wherein the engaged links will readily collapse upon being unlatched. In addition, pin 35 now abuts the edge 36a of slot 36, and the line of centers is now such as to bias the handle in a counter-clockwise or on" direction.

When the circuit breaker is in the On condition and the current passing through the portion of conductor 74 adjacent the bimetallic member rises relatively slowly to excessive values which are conducted for a period of time, the breaker will automatically move into a Tripped condition as seen in FIG. 3. More specifically, the heat generated in the conductor, upon the conduction of the abovementioned excess current, heats up the bimetallic member 115 (See FIG. 2). Upon excessive heating, member 115 rotates in a clockwise direction so that the calibrating screw 117 thereon contacts trip bar 101 and causes the trip bar to rotate correspondingly in a clockwise direction. Rotation of the trip bar 101 extends the trip bar return spring 113 and causes the trip bar extension arm 107 at slot 109 to move out of engagement with the first projection 93 of the trip member 91. Immediately upon such disengagement, the biasing force 121 of the trip spring 123 causes the trip member 91 to rotate in a counter-clockwise direction so that the second projection 95 moves into abutting contact with the projection 67 of the latch with sufficient force to move the latch 55 clockwise as viewed, moving the projections 65 out of engagement with the notches 47 of the links 39a and 39b, permitting collapse of the connecting member 37. The operating spring 83 exerts continuous upward force on the contact arm 71. With the connecting member 37 in unlatched and hence collapsible condition, the spring 83 acting on arm 71 first moves the second end 71b upward into engagement with surface 84 of the cover portion 5 of the breaker casing. Following this, the spring 83 moves the contact arm 71 counterclockwise (about the surface 84) and moves the contact 73 out of engagement with the contact 87 until the first end 71a stops against surface 82 of the cover portion 5 of the casing.

Similarly, when the circuit breaker is in the On condition, if the current passing through the conductor 74 rises to a value indicative of a short circuit condition, the circuit breaker automatically moves into a Tripped condition. More specifically, the field piece will become sufficiently magnetized under the influence of the high current, and thereby exert an attracting force on the armature 119. The armature 119 is thereby caused to rotate into contact with the trip bar 101, rotating the trip bar so as to disengage the extension arm 107 of the trip bar from the trip member 91. Thereafter, the action of the circuit breaker in moving into a Tripped condition is the same as when tripping of the circuit breaker has been caused by the action of the bimetallic member 115.

In a specific embodiment, constructed as disclosed herein, the ratio of total contact pressure (two springs 83) to the force necessary to cause tripping was about 32 to 1.

It should also be observed that in normal, latched condition of the breaker, only a small part of the force of the spring 121 tends to cause rotation of the trip member 91. This is due to the direction of the line of action of the spring 121 as it acts on the trip member 91. Thus initially (when the trip member is in normal position) much of the force of spring 121 acts radially inwardly on the member 91, and does not tend to cause rotation of the member 91.

It is important to note, however, that as the trip member 91 moves toward the latch projection 67, the line of action of the spring 121 changes so that more of its force acts to cause rotation. Thus the spring 121 is more effective to cause unlatching and collapse of the member 37.

This circuit breaker construction, by making it possible for a relatively small force to effect collapse of the latched connecting member 37, makes it possible to achieve a compact mechanism employing relatively small and relatively lightly constructed parts. Further, the desired result is secured with a relatively small number of parts. The use ofa simple compact compression spring 83 instead of over-center springs to supply the force needed to create contact pressure, permits the same force to be achieved within a smaller space than would otherwise be necessary. Additionally, the structural integrating of the operating mechanism and the trip means permits a very compact structure.

While the invention has been shown as incorporated in a two-pole circuit breaker, it is not, of course, limited to such an appication. Thus the mechanism can readily be used with single-pole and three or four-pole circuit breakers. Additionally, it will be obvious to those skilled in the art that other changes and modifications may be made without departing from the invention. It is therefore intended in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States:

1. An electric circuit breaker comprising:

a. an insulating casing;

b. a handle pivotally mounted in the casing;

c. a stationary contact member;

d. a contact member movable into and out of engagement with said stationary contact member;

e. operating spring means acting on said movable contact member;

f. means connecting the handle to the movable contact member, comprising a collapsible connecting member, said connecting member comprising first and second pivotally interconnected links and a latch pivotally connected to said second link and releasably engaging said first link;

a trip member pivotally mounted in the casing;

. means biasing said trip member toward said connecting member;

i. means normally restraining said trip member in a predetermined position out of contact with said connecting member;

j. releasing means mounted in said casing and operable to cause releasing movement of said restraining means;

. said biasing means, upon release of said restraining means, moving said trip member into engagement with said latch member to effect release of said first link from said latch and thereby permit collapse of said connecting member by said operating spring means.

2. An electric circuit breaker as set forth in claim 1 wherein said operating spring means comprises a compression spring disposed in said casing, said movable contact member comprises an elongated structure,

means mounting said structure intermediate its ends to said second link, said movable contact member has a contact adjacent one of said ends and said compression spring acts on said contact member on the opposite side of said mounting means from said contact.

3. An electric circuit breaker as set forth in claim 1 wherein said connecting member further comprises a spring member for biasing said first and second pivotally interconnected links toward abutting contact so as to permit said latch to releasably engage said first link.

4. An electric circuit breaker as set forth in claim 1 wherein said latch releasably and loosely engages said first link to permit relative movement between said first and second links, whereby application of a force to be transmitted by said connecting member through said first and second links puts said links in a slightly collapsed condition with respect to each other.

5. An electric circuit breaker as set forth in claim 1 wherein said releasing means are responsive to the occurrence of a predetermined condition.

6.'An electric circuit breaker as set forth in claim 1 wherein said restraining means comprises a trip bar pivotally mounted in said casing between said trip member and said releasing means, said trip bar biased toward engagement with said trip member and movable away therefrom upon actuation of said releasing means.

7. An electric circuit breaker as set forth in claim 1 wherein said handle and said trip member are mounted for rotation about a common axis of rotation.

8. An electric circuit breaker as set forth in claim 1 wherein the trip member comprises a planar structure having first and second projections at opposite ends thereof; said first projection being engageable with said restraining means and said second projections being engageable with said latch member.

9. A two-pole electric circuit breaker comprising:

a. an insulating casing;

b. a handle pivotally mounted in said casing;

c. a pair of stationary contact members mounted in said casing;

d. a pair of movable contact members mounted in said casing;

e. each of said pair of movable contact members being movable into and out of engagement with corresponding ones of said stationary contact members;

f. operating spring means acting on each of said movable contact members;

g. means connecting said handle to said movable contact member comprising a collapsible connecting member, said connecting member comprising first and second pivotally inter-connected links and a latch pivotally connected to said second link and releasably engaging said first link;

h. a trip member pivotally mounted in the casing;

i. means biasing said trip member toward said connecting member;

j. means normally restraining said trip member in a predetermined position out of contact with said connecting member;

k. releasing means mounted in said casing and operable to cause releasing movement of said restraining means;

I. said biasing means, upon release of said restraining means, moving said trip member into engagement with said latch member to effect release of said first link from said latch and thereby permit collapse of said connecting member by said operating spring means.

a: a a a 

1. An electric circuit breaker comprising: a. an insulating casing; b. a handle pivotally mounted in the casing; c. a stationary contact member; d. a contact member movable into and out of engagement with said stationary contact member; e. operating spring means acting on said movable contact member; f. means connecting the handle to the movable contact member, comprising a collapsible connecting member, said connecting member comprising first and second pivotally interconnected links and a latch pivotally connected to said second link and releasably engaging said first link; g. a trip member pivotally mounted in the casing; h. means biasing said trip member toward said connecting member; i. means normally restraining said trip member in a predetermined position out of contact with said connecting member; j. releasing means mounted in said casing and operable to cause releasing movement of said restraining means; k. said biasing means, upon release of said restraining means, moving said trip member into engagement with said latch member to effect release of said first link from said latch and thereby permit collapse of said connecting member by said operating spring means.
 2. An electric circuit breaker as set forth in claim 1 wherein said operating spring means comprises a compression spring disposed in said casing, said movable contact member comprises an elongated structure, means mounting said structure intermediate its ends to said second link, said movable contact member has a contact adjacent one of said ends and said compression spring acts on said contact member on the opposite side of said mounting means from said contact.
 3. An electric circuit breaker as set forth in claim 1 wherein said connecting member further comprises a spring member for biasing said first and second pivotally interconnected links toward abutting contact so as to permit said latch to releasably engage said first link.
 4. An electric circuit breaker as set forth in claim 1 wherein said latch releasably and loosely engages said first link to permit relative movement between said first and second links, whereby application of a force to be transmitted by said connecting member through said first and second links puts saiD links in a slightly collapsed condition with respect to each other.
 5. An electric circuit breaker as set forth in claim 1 wherein said releasing means are responsive to the occurrence of a predetermined condition.
 6. An electric circuit breaker as set forth in claim 1 wherein said restraining means comprises a trip bar pivotally mounted in said casing between said trip member and said releasing means, said trip bar biased toward engagement with said trip member and movable away therefrom upon actuation of said releasing means.
 7. An electric circuit breaker as set forth in claim 1 wherein said handle and said trip member are mounted for rotation about a common axis of rotation.
 8. An electric circuit breaker as set forth in claim 1 wherein the trip member comprises a planar structure having first and second projections at opposite ends thereof; said first projection being engageable with said restraining means and said second projections being engageable with said latch member.
 9. A two-pole electric circuit breaker comprising: a. an insulating casing; b. a handle pivotally mounted in said casing; c. a pair of stationary contact members mounted in said casing; d. a pair of movable contact members mounted in said casing; e. each of said pair of movable contact members being movable into and out of engagement with corresponding ones of said stationary contact members; f. operating spring means acting on each of said movable contact members; g. means connecting said handle to said movable contact member comprising a collapsible connecting member, said connecting member comprising first and second pivotally inter-connected links and a latch pivotally connected to said second link and releasably engaging said first link; h. a trip member pivotally mounted in the casing; i. means biasing said trip member toward said connecting member; j. means normally restraining said trip member in a predetermined position out of contact with said connecting member; k. releasing means mounted in said casing and operable to cause releasing movement of said restraining means; l. said biasing means, upon release of said restraining means, moving said trip member into engagement with said latch member to effect release of said first link from said latch and thereby permit collapse of said connecting member by said operating spring means. 